diff --git a/Makefile.in b/Makefile.in
index b53cf2c..6e2407f 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -63,6 +63,7 @@ CFLAGS = @CFLAGS@ \
 	 -fPIC \
 	 -I$(TOPDIR) \
 	 -I$(TOPDIR)/kernel-lib \
+	 -I$(TOPDIR)/check \
 	 $(EXTRAWARN_CFLAGS) \
 	 $(DEBUG_CFLAGS_INTERNAL) \
 	 $(EXTRA_CFLAGS)
@@ -93,7 +94,8 @@ objects = ctree.o disk-io.o kernel-lib/radix-tree.o extent-tree.o print-tree.o \
 	  extent-cache.o extent_io.o volumes.o utils.o repair.o \
 	  qgroup.o raid56.o free-space-cache.o kernel-lib/list_sort.o props.o \
 	  ulist.o qgroup-verify.o backref.o string-table.o task-utils.o \
-	  inode.o file.o find-root.o free-space-tree.o help.o
+	  inode.o file.o find-root.o free-space-tree.o help.o \
+	  check/csum.o
 cmds_objects = cmds-subvolume.o cmds-filesystem.o cmds-device.o cmds-scrub.o \
 	       cmds-inspect.o cmds-balance.o cmds-send.o cmds-receive.o \
 	       cmds-quota.o cmds-qgroup.o cmds-replace.o cmds-check.o \
@@ -463,7 +465,7 @@ clean-all: clean clean-doc clean-gen
 clean: $(CLEANDIRS)
 	@echo "Cleaning"
 	$(Q)$(RM) -f -- $(progs) cscope.out *.o *.o.d \
-		kernel-lib/*.o kernel-lib/*.o.d \
+		kernel-lib/*.o kernel-lib/*.o.d check/*.o check/*.o.d \
 	      dir-test ioctl-test quick-test send-test library-test library-test-static \
 	      btrfs.static mkfs.btrfs.static \
 	      $(check_defs) \
diff --git a/check/check.h b/check/check.h
new file mode 100644
index 0000000..61d1cac
--- /dev/null
+++ b/check/check.h
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2016 Fujitsu.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+/* check/csum.c */
+int btrfs_read_one_data_csum(struct btrfs_fs_info *fs_info, u64 bytenr,
+			     void *csum_ret);
diff --git a/check/csum.c b/check/csum.c
new file mode 100644
index 0000000..53195ea
--- /dev/null
+++ b/check/csum.c
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2016 Fujitsu.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include "ctree.h"
+#include "utils.h"
+/*
+ * TODO:
+ * 1) Add write support for csum
+ *    So we can write new data extents and add csum into csum tree
+ * 2) Add csum range search function
+ *    So we don't need to search csum tree in a per-sectorsize loop.
+ */
+
+int btrfs_read_one_data_csum(struct btrfs_fs_info *fs_info, u64 bytenr,
+			     void *csum_ret)
+{
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	struct btrfs_root *csum_root = fs_info->csum_root;
+	u32 item_offset;
+	u32 item_size;
+	u32 final_offset;
+	u32 sectorsize = fs_info->tree_root->sectorsize;
+	u16 csum_size = btrfs_super_csum_size(fs_info->super_copy);
+	int ret;
+
+	if (!csum_ret) {
+		error("wrong parameter for %s", __func__);
+		return -EINVAL;
+	}
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
+	key.type = BTRFS_EXTENT_CSUM_KEY;
+	key.offset = bytenr;
+
+	ret = btrfs_search_slot(NULL, csum_root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+	if (ret == 0) {
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+		if (!IS_ALIGNED(key.offset, sectorsize)) {
+			error("csum item bytenr %llu is not aligned to %u",
+			      key.offset, sectorsize);
+			ret = -EIO;
+			goto out;
+		}
+		u32 offset = btrfs_item_ptr_offset(path->nodes[0],
+						      path->slots[0]);
+
+		read_extent_buffer(path->nodes[0], csum_ret, offset, csum_size);
+		goto out;
+	}
+	ret = btrfs_previous_item(csum_root, path, BTRFS_EXTENT_CSUM_OBJECTID,
+				  BTRFS_EXTENT_CSUM_KEY);
+	if (ret)
+		goto out;
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+	if (!IS_ALIGNED(key.offset, sectorsize)) {
+		error("csum item bytenr %llu is not aligned to %u",
+		      key.offset, sectorsize);
+		ret = -EIO;
+		goto out;
+	}
+	item_offset = btrfs_item_ptr_offset(path->nodes[0], path->slots[0]);
+	item_size = btrfs_item_size_nr(path->nodes[0], path->slots[0]);
+	if (key.offset + item_size / csum_size * sectorsize <= bytenr) {
+		ret = 1;
+		goto out;
+	}
+
+	final_offset = (bytenr - key.offset) / sectorsize * csum_size +
+		       item_offset;
+	read_extent_buffer(path->nodes[0], csum_ret, final_offset, csum_size);
+	ret = 0;
+out:
+	btrfs_free_path(path);
+	return ret;
+};
